Page 83 - Introduction to Marine Engineering

70 Steam turbines and gearing

Adaptor
plate

Emergency

Rotor or
^ pinion
flange
Membrane
Figure S.I5 Flexible coupling

Operating procedures

The steam turbine requires a considerable period for warming-through
prior to any manoeuvring taking place. The high-speed operation of the
turbine and its simply supported rotor also require great care during
manoeuvring operations.

Warming-through a steam turbine
First open all the turbine-casing and main steam-line drain valves and
ensure that all the steam control valves at the manoeuvring station and
around the turbine are closed. All bled steam-line drain valves should be
opened. Start the lubricating oil pump and see that the oil is flowing
freely to each bearing and gear sprayer, venting off air if necessary and
check that the gravity tank is overflowing.
Obtain clearance from the bridge to turn the shaft. Engage the
turning gear and rotate the turbines in each direction.
Start the sea water circulating pump for the main condenser. Then
start the condensate extraction pump with the air ejector recirculation
valve wide open. Open the manoeuvring valve bypass or 'warming
through' valve, if fitted. This allows a small quantity of steam to pass
through the turbine and heat it. Raising a small vacuum in the
condenser will assist this warming through. The turbines should be
continuously turned with the turning gear until a temperature of about
75°C is reached at the LP turbine inlet after about one hour. The
expansion arrangements on the turbine to allow freedom of movement
should be checked.
Gland sealing steam should now be partially opened up and the
vacuum increased. The turning gear should now be disengaged.